Ohio-made bolts need OK for Calif. bridge to open

Sunday

Apr 28, 2013 at 12:01 AMApr 28, 2013 at 3:29 PM

SAN FRANCISCO - Steel bolts on the new eastern span of the San Francisco-Oakland Bay Bridge made by the same company that supplied 32 rods that failed when they were tightened must undergo rigorous testing to determine whether they also are at risk of cracking, state officials said last week.

SAN FRANCISCO — Steel bolts on the new eastern span of the San Francisco-Oakland Bay Bridge made by the same company that supplied 32 rods that failed when they were tightened must undergo rigorous testing to determine whether they also are at risk of cracking, state officials said last week.

The outcome of those tests, expected within two weeks, will determine whether the $6.4 billion span will open to traffic the day after Labor Day as scheduled, California Department of Transportation Director Malcolm Dougherty said. He had briefed Bay Area transportation officials about the broken-bolt investigation at a meeting in Oakland.

Dyson Corp., of Painesville, Ohio, supplied the 32 bolts that failed last month and an additional batch of 192 rods delivered in 2010. Dougherty said visual inspections have revealed no problems with the 2010 bolts. Like the 32 that arrived at the span in 2008, those bolts are intended to hold down seismic-safety structures.

Further tests to gauge their long-term vulnerability to cracking will be the “key driver” in determining whether the bridge opens on Sept. 3, Dougherty said.The 32 failed bolts, which cracked when they were tightened, were among 96 bolts delivered in 2008 that Caltrans has written off as unusable. The bolts were covered by the bridge roadways soon after being installed and no longer are accessible, so Caltrans is considering adding a metal collar around the seismic-stability structures to do the bolts’ job.

The 2008 bolts are thought to have been weakened by hydrogen that was able to attack because the steel was near the maximum hardness level allowed under industry standards. The harder the steel, the more vulnerable it is to hydrogen.

Caltrans officials say they think the bolts delivered by Dyson in 2010 were not as hard and might be better able to resist hydrogen, which is abundant in the marine air.

Steve Heminger, executive director of the Metropolitan Transportation Commission, said stress corrosion is a real threat to the 2010 bolts.

“These bolts will be under very high tension for a very long time,” he said, “and they will be in an environment that is swimming in hydrogen, and they are susceptible to it because they are high-strength bolts.”

He said that if the 2010 bolts prove to be vulnerable, they could be replaced over time after the bridge opens.

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